1. Field of the Invention
This invention relates to a gang-punch or other punch apparatus and method for punching holes in thin sheet material such as ceramic greensheets used in multilayer ceramic electronic component fabrication and, more particularly, to punch pins for use with the apparatus and a method and apparatus for making the punch pins.
2. Description of Related Art
In the manufacture of multilayer ceramic (MLC) substrates for integrated circuit semiconductor package structures, a plurality of green ceramic sheets (commonly termed greensheets) is formed by doctor blading a slurry containing a resin binder, a particulate ceramic material, solvents and a plasticizer, drying the doctor bladed sheet and cutting it into appropriate size sheets. Holes, commonly termed vias, are then punched in the greensheets to facilitate performing electrical interconnections through the sheet. Electrically conductive paste is deposited in the holes and in appropriate circuitry patterns on the surface of the greensheets, the sheets stacked and laminated, and the assembly subsequently fired at a sintering temperature.
The formation of the vias in the ceramic material is accomplished in its green state. Prior to being fired, the greensheets are easily deformed and the precision with which the via holes are formed is greatly dependent upon the use of apparatus which minimize distortion or disruption to the structural integrity of the greensheet other than forming the via hole. With the size of electrical components constantly being reduced through technical improvement the positioning of the via holes in the ceramic greensheets is becoming ever more restrictive. Further, with the increase in the quantity of the electronic circuits needed to make the electronic component package, the requirement for a larger number of vias per unit area of substrate is evident.
Large numbers of holes must be punched into a greensheet with a high degree of precision in order to properly position the hole. At the same time, this punching operation must occur very rapidly in order to produce the large numbers of greensheets that are necessary in the mass production of multilayer ceramic electronic components.
A significant portion of the costs associated in manufacturing ceramic packages can be attributed to that of punching vias in greensheets. The following factors play a major role in accounting for these costs: 1) the high cost for punch/die sets customized to a specific product; 2) customized punch/die sets steps/repeats numerous times up to several thousand cycles to punch a single sheet, resulting in low throughput; 3) non-customized punch die sets have very low throughput for non-grid product (up to 20 k cycles per sheet); and 4) the long lead-time associated with customized punch die set fabrication precludes early introduction of a new product.
One method for punching greensheets is using a gangpunch apparatus. A gang-punch is a punch/die set where all the punches for a particular ceramic greensheet layer are rigidly and permanently mounted in a rigid plate. This mounting may be accomplished using adhesive (epoxies, etc.) or press fitting. This permanent mounting makes punch placement to repair broken or worn punches difficult and expensive. The gang-punch is used to punch the entire sheet (layer) with a single stroke. A gang-punch has very high throughput and is cost effective for very high volume products.
A number of attempts have been made to provide "gang-punch" apparatus which will economically and efficiently provide the means to make via openings in greensheets. One type apparatus utilizes an interposer mask which contains hole openings where holes are desired to be punched. In these types apparatus, a plurality of punch elements arranged in a grid are arranged over the greensheet which is covered by the interposer mask. When the punch elements contact the interposer mask as the punch head is moved downwardly, the hole will be punched where the openings occur since the punch element would pass through the openings in the interposer mask and through the ceramic greensheet. In other areas covered by interposer mask, i.e., where holes are not desired, the interposer mask will cause the punch element to be retracted into the head. Such apparatus are shown in IBM Technical Disclosure Bulletins, Vol. 16, No. 12, May 1974; Vol. 19, No. 4, September 1976 and Vol. 26, No. 10A, March 1984. Other punch apparatus are shown in U.S. Pat. Nos. 4,872,381; 4,425,829; 5,024,127; 5,090,284; and 5,233,895. In U.S. Pat. No. 4,872,381, supra, for example, a programmable magnetic repulsion punching apparatus is shown. A progressive gang-punch is shown in IBM Technical Disclosure Bulletin Vol. 15, No. 2, July 1972 wherein a gang-punch is shown utilizing steel balls at locations of punches to be punched on the surface of the punch head which when a roller traverses the top of the punch head vias are punched only where steel balls are located. The disclosures of the above publications and patents are hereby incorporated by reference.
A significant factor in the cost of gang-punching is the cost of the punch pins since thousands of punch pins are typically needed for use with a gang-punch apparatus. Conventional gang punch pins are typically about 1/2 inch long and have a diameter of about 0.003 inch to 0.008 inch and are permanently and rigidly affixed to the head. They are relatively expensive (about $1 each) and difficult to replace. Headed punches whose head is used to retain the punch pin in the punch head, allowing easy removal when necessary, are even more expensive (about $1-7 each) . The punch pins of the present invention can be fabricated for typically about $ 0.01 each.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a cost effective (typically about $0.01 each) and efficient method for making headed punch pins for use in punching apparatus such as a gang-punch apparatus for punching greensheets.
It is a further object of the present invention to provide an apparatus for making headed punch pins for use in punching apparatus such as a gang-punch apparatus for punching greensheets.
An additional object of the invention is to provide headed punch pins for use in methods and apparatus for punching vias in greensheets.
Other objects and advantages of the present invention will be readily apparent from the following description.